A common OFDM receiver is shown in FIG. 8a. The OFDM-signal is received by an antenna 100 and fed via an amplification and pre-processing circuit 101 as RF- or n-IF-signal to a multiplier 102 that down-converts the received, amplified and pre-processed OFDM-signal into an IF-signal on basis of a demodulation signal from an oscillator 103. This IF-signal is input to an IQ-demodulator 104 that additionally receives a demodulating signal from an oscillator 105 and produces the complex spectrum of the demodulated OFDM-signal, i.e. an inphase signal I and a quadrature signal Q. These both signals are input to an analog-to-digital converter 106 to leave the analog stage of the receiver and to enter its digital stage wherein first a Fast Fourier Transformation is carried out with a FFT-unit 107 before a demapper 108 produces a baseband signal for the further processing. It can be seen that an FT-process is implemented within the digital stage which therefore needs a relatively high processing power.
As OFDM modulation schemes seem to be widely accepted for different public broadcasting systems like DAB, DVB-T and private WLANs as a modulation scheme the requirements in regard to the needed bandwidth increase and therefore larger number of carriers are needed, which can be hardly handled by one digital processor. Therefore, to cope with this coming situation, different paralleling techniques have to be incorporated into future OFDM telecommunication devices. Such a block processing (parallel to serial conversion and vice versa) means that a large amount of processing power might be necessary and a large power consumption might arise as well as increased printed circuit board layout requirements have to be thought of.
On the other hand, analog processing techniques to perform the Fourier Transformation are known, e.g. from U.S. Pat. No. 5,226,038 which discloses a method and apparatus for converting electronic signals from frequency-division multiplex format into time-division multiplex format to perform an antenna beam forming and thereafter to perform a conversion from time-division multiplex-format into frequency-division multiplex-format while retaining substantially all phase and amplitude information of a band-limited continuous signal. This document describes the use of the well-known multiplication (M), convolution (C), multiplication (M) and CMC algorithm to perform siuch transformations. Furtheron, it is described that a Fourier Transformation of an analog signal sequence can be performed either by the MCM algorithm under use of chirp signals or the CMC algorithm with such signals. In this context also a reference is given to Fourier transform processors based on Surface Acoustic Wave filters.
Furtheron, a description given by the Phonon Corporation discloses to assemble spectrum analyzers and Fourier transformers from sets of dispersive delay lines to perform a scanning for determining on which frequencies signals are present. This description discloses that applications of such systems are also advanced communiation techniques, since they can process in real time at rates far in excess of current digital techniques, with relatively little size, weight and power.
The mathematical foundations for the MCM operation is shown in the following. Under consideration of the Fourier Transformation S(f) of a signal s(t) which is bandlimited to Be and of a maximum duration Te, the Fourier Transformation integral can be written in the form of the “chirp transform algorithm”:
            Operation      :                          ⁢                          ⁢              S        ⁡                  (          f          )                      =                  S        ⁡                  (                                    -              a                        ·            t                    )                    =                        (                                    (                                                s                  ⁡                                      (                    t                    )                                                  ·                                  Re                  ⁡                                      (                    t                    )                                                              )                        *                          Re              ⁡                              (                t                )                                              )                ·                  (          t          )                      ,          ⁢                         ⁢          M      ⁢                          ⁢      C      ⁢                          ⁢      M      where · is multiplication, * is convolution, a=Be/Te is a scale factor, Re(t) is a chirp signal with the chirp rate−a=−Be/Te and Rc(t) is the impulse response of an entity providing analog convolution with a length Tc=2Te and a chirp rate a=Bc/Tc.
However, no realization of a telecommunication device, e.g. an OFDM receiver as shown in FIG. 8a, using such analog Fourier transformers for modulation and/or demodulation purposes is known.